Fluid solids systems with vapor containing solids streams typically require the contained solids to be retained in certain equipment while the vapor product, essentially free of solids, is processed in downstream equipment. It is desirable in these systems that the solids be as completely removed as possible from the vapor and retained in the fluid solids portion of the process. High solids retention in the fluid solids portion of the process is particularly desirable in cases in which the solids may be expensive, may contaminate the vapor product or downstream vapor process handling systems, and increase the capital and operating costs of downstream particulate capture devices such as wet gas scrubbers, electrostatic precipitators, or filters. Therefore, improvements in high efficiency solids/vapor separation systems are of particular interest.
In reactor systems that use small particle catalysts, the loss of catalyst particles during operation means that additional catalyst has to be added during operation to make up for the catalyst loss. Particularly in cases where the cost of catalyst is substantially high, even marginal improvements in solid particle retention can lead to substantial reductions in operating costs.
U.S. Pat. No. 2,934,494 to Kleiber describes a process for recovering finely divided solids in a fluidized bed reactor using at least two cyclone separator stages. In Kleiber, the velocity in the second cyclone stage is at least 50% greater than the velocity in the first cyclone stage, and the velocities of the first cyclone stage range from 50 to 70 ft/sec. The process provided in Kleiber maintains a fines content in the catalyst inventory, commonly referred to as equilibrium catalyst or e-cat, of between 9-30% in the reactor.
What is needed is an improved process for removing solid particles in gas-solids reactors, particularly in reaction systems that use molecular sieve type catalysts. Especially desirable processes would include those that provide for a higher retention rate of solid particles, and those that have minimal or no impact on the efficiency of the reaction being carried out in the reactor. Such processes would also be advantageously carried out with little or no damage to the catalyst; in particular, with little to no physical damage, thereby reducing particle attrition during operation.